The present invention relates to the technical field of increasing recovery of crude oil from a subterranean hydrocarbon-containing formation using a fluid, in particular, an acid fluid. These methods are useful in the petroleum and associated industries. When crude oil production declines, there are a number of causes for the decline in production. Two reasons for a decline in oil production are (1) a reduction in the permeability of the oil “reservoir” or (2) the invasion of this reservoir by the water contained in a lower layer.
A reduction in permeability is typically due to the entrainment of fines, by the flow of the oil, towards the production well. Around this well, these particles accumulate and gradually plug the natural pores in the rock. The oil can then no longer flow out at an efficient rate through this well. These particles can be of various origins (e.g., type of rock, damage to the formation, progressive deterioration of the rock, etc.).
In order to remove these particles and improve the mobility of the oil in the formation, an acidic fluid can be injected into the well where some of the particles and some of the rock in the formation are partially soluble in this acidic fluid. Thus, this well stimulation method can cause these particles and rock to partially dissolve, and make the rock of the formation more porous thereby increasing the mobility of the oil in the formation and increasing well production.
Further, the invasion by water of the oil producing zone is due to the difference in viscosity between oil and water. Since water is less viscous than oil, it is more mobile than the oil, and once the rocks in the formation become more porous, the water of the aqueous solution follows the path of least resistance. In order to provide a greater area where the acidic solution improves the permeability of the rock in the formation, various agents are included in the acidic fluid to divert the acidic fluid into neighboring areas of the formation to maximize contact of the acid with the rock. A continuing need exists for alternative agents for acid diversion in these situations that are easier to apply and more environmentally friendly.